pespin has uploaded this change for review.

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tun_device: Avoid deadlocks logging while thread is cancelled

We cannot garantee that LOGP will not end up calling a syscall which can
be a cancellation point. Since the syscall will be probably called while
having the logging mutex locked, an eventuall cancellation of the thread
would leave the logging mutex locked forever, hence making all other
threads deadlock as soon as they try to write anything to the log.

Change-Id: I72a0b536c8f39857960f132a5b84cdf5b8519732
---
M daemon/tun_device.c
1 file changed, 11 insertions(+), 0 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/osmo-uecups refs/changes/69/27769/1

diff --git a/daemon/tun_device.c b/daemon/tun_device.c
index 5993856..e9c0400 100644
--- a/daemon/tun_device.c
+++ b/daemon/tun_device.c
@@ -139,12 +139,17 @@
 	uint8_t *buffer = base_buffer + sizeof(struct gtp1_header);
 
 	struct sockaddr_storage daddr;
+	int old_cancelst_unused;
 
 	/* initialize the fixed part of the GTP header */
 	gtph->flags = 0x30;
 	gtph->type = GTP_TPDU;
 
 	pthread_cleanup_push(tun_device_pthread_cleanup_routine, tun);
+	/* IMPORTANT!: All logging functions in this function block must be called with
+	 * PTHREAD_CANCEL_DISABLE set, otherwise the thread could be cancelled while
+	 * holding the logging mutex, hence causing deadlock with main (or other)
+	 * thread. */
 
 	while (1) {
 		struct gtp_tunnel *t;
@@ -154,6 +159,7 @@
 		/* 1) read from tun */
 		rc = read(tun->fd, buffer, MAX_UDP_PACKET);
 		if (rc < 0) {
+			pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old_cancelst_unused);
 			LOGTUN(tun, LOGL_FATAL, "Error readingfrom tun device: %s\n", strerror(errno));
 			exit(1);
 		}
@@ -162,8 +168,10 @@
 
 		rc = parse_pkt(&pinfo, buffer, nread);
 		if (rc < 0) {
+			pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old_cancelst_unused);
 			LOGTUN(tun, LOGL_NOTICE, "Error parsing IP packet: %s\n",
 				osmo_hexdump(buffer, nread));
+			pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &old_cancelst_unused);
 			continue;
 		}
 
@@ -181,7 +189,9 @@
 			getnameinfo((const struct sockaddr *)&pinfo.saddr,
 				    sizeof(pinfo.saddr), host, sizeof(host), port, sizeof(port),
 				    NI_NUMERICHOST | NI_NUMERICSERV);
+			pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old_cancelst_unused);
 			LOGTUN(tun, LOGL_NOTICE, "No tunnel found for source address %s:%s\n", host, port);
+			pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &old_cancelst_unused);
 			continue;
 		}
 		outfd = t->gtp_ep->fd;
@@ -193,6 +203,7 @@
 		rc = sendto(outfd, base_buffer, nread+sizeof(*gtph), 0,
 			    (struct sockaddr *)&daddr, sizeof(daddr));
 		if (rc < 0) {
+			pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old_cancelst_unused);
 			LOGTUN(tun, LOGL_FATAL, "Error Writing to UDP socket: %s\n", strerror(errno));
 			exit(1);
 		}

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